This invention is directed to certain hafnium complexes, to catalyst compositions comprising the same, and to addition polymerization processes, especially olefin polymerization processes, using such hafnium complexes as one component of a coordination polymerization catalyst composition.
Advances in polymerization and catalysis have resulted in the capability to produce many new polymers having improved physical and chemical properties useful in a wide variety of superior products and applications. With the development of new catalysts the choice of polymerization-type (solution, slurry, high pressure or gas phase) for producing a particular polymer has been greatly expanded. Also, advances in polymerization technology have provided more efficient, highly productive and economically enhanced processes. Recently, several new disclosures related to metal complexes based on polyvalent metal-centered, heteroaryl donor ligands have published. Among these are U.S. Pat. Nos. 6,103,657, 6,320,005, 6,653,417, 6,637,660, 6,906,160, 6,919,407, 6,927,256, 6,953,764, US-A-2002/0142912, US-A-2004/0220050, US-A-2004/0005984, EP-A-874,005, EP-A-791,609, WO 2000/020377, WO2001/30860, WO2001/46201, WO2002/24331, and WO 2002/038628.
Regardless of the technological advances in the polyolefin industry afforded by this new class of catalyst, common problems, as well as new challenges associated with process operability, exist. For example, known Group 4 metal complexes based on donor ligands are often of limited solubility in aliphatic hydrocarbon solvents, which in a solution polymerization can result in the need to handle increased volumes of catalyst solution or employ aromatic solvents such as toluene. In addition, the use of higher polymerization temperatures is desired in order to improve process efficiency. Disadvantageously however, higher reaction temperatures can reduce activity as well as generate polymers having reduced molecular weight, tacticity or crystallinity, especially when highly isotactic polymers, are produced.
Thus, it would be advantageous to provide a solution polymerization process for the polymerization of olefin monomers employing specific metal complexes based on donor ligands that are capable of operation at high temperatures and efficiencies and having improved solubility in aliphatic hydrocarbon solvents. Moreover, it would be advantageous to provide a solution polymerization process for preparing tactic polymers, especially isotactic homopolymers and copolymers comprising propylene and/or a C4-20 olefin and optionally ethylene, that is capable of operation at high temperatures and adapted to produce polymers having a relatively high molecular weight, tacticity and/or crystallinity.